I saw some people complaining about the Attack on Titan anime earlier because it changed some parts from the manga. I on the other had would praise the animation staff, they cleaned up Attack on Titan very nicely, the original manga is kind of hard to follow at times, the anime also added quite a few supplementary scenes that were not in the manga that help you understand the characters better./quote]

Hmm well my experience is limited, with Anime only being just over a year and Manga at 6 months. I only read 2 Manga so far that have had adaptations after I started reading which are this seasons runners Nisekoi and D-Frag. Both of which so far are getting pretty good and faithful adaptations.

YuYu Hakusho is actually a better anime than manga if only because the anime ending is miles above the manga's. I felt the manga kinda just cut off and ended with Kurama filling me in on the aftermath. The anime greatly expanded upon the ending, putting a lot more fight scenes and we actually got to see Keiko and Yuskue meet back up (which is another thing that Kurama had to explain to the reader rather than show it).

Trigun actually is a really good adaption; the changes made sense and the overall themes were still greatly conveyed to the watcher.

The new Jojo's anime has been utterly fantastic, better than the manga in my opinion; hyped for Stardust Crusaders.

Gunslinger Girl, Black Lagoon, Birdy the Mighty: Decode, Gantz, etc. -- all had good anime adaptations. As for which are better, I'm not going to go there as I think their have both their own strengths and weaknesses compared to their source materials. But, as for what I liked in the adaptations that weren't in the manga (just few examples of many):

In Gunslinger Girl:

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The episode in the anime that focused on Elsa and her handler that incorporated them more into the story than the manga did. It gave them more character.

In Black Lagoon:

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Roberta's disfigurement at the end of Blood Trail.

In Birdy the Mighty: Decode:

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Basically, the whole plot.

In Gantz:

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The depiction of Tetsuo, the leader of that biker gang. He has a better personality.